Voiceover: In this video I
want to just introduce some of the anatomy involved
in neurotransmitters. Recall that neurotransmitters
are molecules that communicate between neurons and their target cells
and chemical synapses. And some neurotransmitters
are released by neurons distributed widely throughout
the nervous system, while others are specific
to certain areas. For examples of some neurotransmitters that are released by neurons distributed throughout the nervous system,
the first one is glutamate, which is the most common
excitatory neurotransmitter of the entire nervous system. Then there's GABA, which is short for gamma-aminobutyric acid, and glycene, and these are the most common
inhibitory neurotransmitters of the nervous system, GABA in the brain and glycene in the spinal
cord in particular. Neurons releasing these neurotransmitters are widely distributed
through the nervous system, and these neurotransmitters
are really involved in most functions of the nervous system. Next I want to just introduce some of these areas of the
brain that have collections of neurons that send axons diffusely to release specific neurotransmitters onto widespread areas
of the cerebral cortex. And often other areas as well, but these widespread projections
to the cerebral cortex, let me just represent these by a few axons coming up toward the cerebral cortex, and these widespread
projections that are dumping a bunch of a specific
kind of neurotransmitter all over your big areas
of the cerebral cortex are really important for a bunch of the higher functions
of the nervous system, including the cognition,
emotion, and consciousness. So let me start
introducing a few of these, and I'm going to start with glutamate, because there are specific areas in the reticular formation
of the brain stem and parts of the thalamus
that project axons diffusely up to the cerebral cortex
and release glutamate all over neurons of the cerebral cortex. And this collection of neurons that has this diffuse projection of glutamate to the cerebral cortex, we call this the reticular
activating system. And this is actually
required for consciousness. Without this system, there
usually is no consciousness. The next one I want to
mention is acetylcholine. There are certain nuclei
in the frontal lobe that actually send diffuse
projections up to a number of areas in the cerebral
cortex, releasing acetylcholine. These are called the basalis
nucleus and the septal nuclei. The next one I want to
mention is histamine, and there are a number of
neurons in the hypothalamus that send projections to release histamine all over the cerebral cortex. So the hypothalamus is
here, and these neurons send these diffuse projections up to the cerebral cortex
to release histamine. Next is norepinephrine,
and there's an area here in the pons where there are a bunch of neurons that send diffuse projections of norepinephrine up
to the cerebral cortex. That area is called the locus ceruleus, and I've seen a few different
ways of spelling this, but this is the one I'm familiar with. I'm sure any of them are fine. Then there's serotonin,
and there are a number of nuclei at all levels of the brain stem, up here in the midbrain,
down here in the pons, and in the medulla that are
all called the raphe nuclei. These raphe nuclei release serotonin, and my understanding is
that it's mostly the ones that are higher up that
send diffuse projections up to the cerebral cortex
to release serotonin, and that these raphe
nuclei also send serotonin to other part of the nervous system. And last up, although I'm
sure there's probably more, but last up that I want to talk about of these diffuse projection systems releasing neurotransmitters
onto the cerebral cortex, involves the neurotransmitter dopamine. For dopamine, there's an
area here-ish in the midbrain that diffusely projects dopamine
onto the cerebral cortex, and that area is called
the ventral tegmental area. I'll just right VTA for short for the ventral tegmental area. So all of these diffuse projection systems sending neurotransmitters
through widespread areas of the cerebral cortex
are, again, very important to the higher functions
of the nervous system, like aspects of cognition and
emotion and consciousness, and many psychiatric disorders appear to involve dysfunction of
these neurotransmitter systems. Many of the psychoactive
medications appear to influence neurotransmitter
release from these diffuse projection systems
to the cerebral cortex. Now, for dopamine in particular, there are a couple of
other projection systems of dopamine that aren't
to the cerebral cortex, but that are important for
functions of the nervous system and can become problems for medications that affect dopamine neurotransmission. One of these is right next to the ventral tegmental
area in the midbrain. I'll actually draw them overlapping because they're so close together. And it sends axons releasing dopamine to a couple of nuclei deep
in the cerebral hemisphere, and these are all actually
parts of the basal ganglia. So this collection of
neurons in the midbrain that is projecting dopamine is
called the substantia nigra. It's actually projecting dopamine up to another part of the basal
ganglia called the striatum. If there's some problem with this system, some problem with the substantia nigra getting dopamine to the striatum, that appears to be what happens
with Parkinson's disease. I won't go more into that now, but that's very important
for Parkinson's disease and other disorders
that have Parkinsonism, or the symptoms and signs
of Parkinson's disease. There are also dopaminergic
neurons in the hypothalamus. These dopaminergic neurons
in the hypothalamus are actually sending dopamine down to the pituitary gland
to control the release of one of the hormones
in the pituitary gland. I won't go any more into that, but that's another important
dopamine projection system. So all of that's in the
central nervous system in the brain and the spinal cord, but there are neurotransmitters
involved in the function of the peripheral nervous
system too, all the nerves going out to structures
in the rest of the body. Our main ones there are
acetylcholine and norepinephrine. Acetylcholine has several jobs. It's the neurotransmitter released from lower motor neurons
coming out of the spinal cord or the brain stem, and their
axons will then synapse on skeletal muscle cells
and release acetylcholine, that's the neurotransmitter they use. But acetylcholine is also involved in the function of the
autonomic nervous system. Let me just write ANS for short for autonomic nervous system. Most of the neurons of the
autonomic nervous system release acetylcholine as
their neurotransmitter, and a smaller number of neurons of the autonomic nervous system release norepinephrine as
their neurotransmitter. So I'll stop there in my
overview of the anatomy of neurotransmitters
to just give you a feel for how many different
types of neurotransmitters are located in lots of different areas. And I just want to make the point that some neurotransmitters
are used widely throughout the nervous
system, whereas others have these more kind of
discrete collections of neurons that are either projecting widely to areas of the nervous system
like the cerebral cortex, or more specifically
between one specific area and another specific area.